sedimentary

Dark flint or chert

Microcrystalline quartz (SiO₂), chiefly chalcedony with possible moganite

AI-generated identification · may be incorrect

Typically black, gray, brown, or olive-gray; waxy to dull luster; conchoidal fracture and no visible cleavage. Mohs hardness is about 6.5–7; the specimen appears fine-grained, opaque, and naturally fractured or roughly worked.

Identified September 15, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica-rich groundwater or biogenic silica replaces carbonate sediments, commonly during the Paleozoic–Cenozoic eras; flint is a dark variety associated especially with chalk. Common settings include limestone beds, nodules, gravel deposits, and glacial sediments.

Uses & applications

Used historically for sharp tools, arrowheads, fire-starting, and construction aggregate; attractive polished pieces are sold as lapidary material. It is generally inexpensive unless archaeologically significant or unusually patterned.

Geological facts

Conchoidal fracture produces sharp edges, making flint important in prehistoric technology. The image may also show minor iron-oxide staining or weathering, but it does not display the typical glassy translucence of obsidian.

Field identification & locations

Identify it by testing for glass-like conchoidal fracture, lack of cleavage, and ability to scratch ordinary glass; acid generally produces no reaction unless carbonate material is present. Common sources include England, France, the Baltic region, Texas, Kansas, and many gravel deposits.